The reasons for surgical intervention for fuse the occipital cervical joints are varied, but the reasons can be categorized as falling within one of five fundamental categories.                Neurologic Disorder;        Mechanical Changes to the Spinal Column resulting in pain;        Instability;        Deformity; and        Pathological Reasons-such as tumors or infection.        
The skull may be viewed as a continuation of the spinal column. Sometimes surgical intervention is justified to fuse a series of one or more vertebrae in the spinal column. Likewise, there are situations that justify fusing the occipital portion of the skull to at least the C1 vertebra and often to the C2 vertebra or the C2 and C3 vertebrae. Some situations require fusing past the C3 vertebra possibly as far as the upper thoracic vertebrae.
Surgery is only justified when non-operative treatments are either ineffective or not an option. A non-exhaustive list of the specific reasons for surgical intervention that fall within these broad categories includes the following reasons. Instability of the occipitocervical joints may result from, for example, trauma (to the ligamentous structures of the craniocervical junction; fracture, or dislocation); degenerative disease processes (e.g., rheumatoid arthritis with vertical migration of the odontoid; degenerative spondylosis; spondylolisthesis; spinal stenosis); tumor; infection, or congenital malformation. Instability of the cervicocranium may lead to significant pathological translation, longitudinal displacement, or basilar invagination. Cervical cord compression and trauma to the spinal cord or the brainstem can result in respiratory distress, pain, cranial nerve dysfunction, paresis and paralysis, or even sudden death. Therefore, the need for occipitocervical stabilization may exist for patients with pathological instability.
Occipitocervical arthrodesis, or fusion, provides needed biomechanical stability and is a therapy used to treat such instability. Occipitocervical arthrodesis comprises decortication, deployment of appropriate spinal instrumentation and assemblies, and placement of structural and supplemental bone graft around the decorticated bony elements of the cranium and cervical vertebrae. In some instances the therapy may extend beyond the cervical spine to more caudal vertebral levels. The objective is to create a stable biomechanical environment and provide the biological requirements for osseous fusion. Adequate anterior spinal cord support for load sharing with the posterior implant construct is recommended. Adequate decompression of the neurological structures, where indicated, and recreation of normal sagittal and coronal alignment are prerequisites prior to an arthrodesis procedure. Due to the nature and location of this surgical procedure, adverse events can be serious and cause further neurological injury or impairment; vascular injury; cerebrospinal fluid (CSF) egress; infection; instrumentation failure; pseudoarthrosis; continued instability, deformity, and pain.
Occipitocervical fixation has been achieved using a variety of techniques to provide stabilization and/or alignment of the base of the skull with respect to the neck, followed by fusion, or arthrodesis by means of bone graft insertion. Existing surgical techniques and assemblies known in the art include posterior wiring/rods (for example, sublaminar and interspinous wires); screws/rods; hooks/rods; screws/plates; wires/plates, and posterior wiring with onlay graft.
Within these groups, there are various construct configurations, including hybrid systems. Initially, methods for achieving posterior occipitocervical stabilization included fusion and simple wire techniques that required periods of traction followed by a halo, and rod and wire assemblies that were more stable, but continued to have difficulty preventing axial loads due to the rods pistoning through the sublaminar wires.
While occipito-cervical-thoracic stabilization procedures, and in particular posterior occipitocervical fusion surgical implants, instrumentation, and techniques, continue to evolve in the pursuit of improvements in clinical outcomes (e.g., the highest fusion rate with the shortest time to fusion and improvement in neurological function), and in simplicity of use, notwithstanding, there remains a need for ongoing advancements in plate, rod and screw assemblies leading to progress in the surgical management of complex cervical disorders, to accommodate an increased spectrum of anatomical variations, to enable simplicity of instrumentation placement, and to avoid certain adverse events such as loss of spinal alignment, in order to achieve more rigid stabilization in a wider variety of spinal diseases.
More particularly, plate and screw assemblies known in the art have multiple limitations, including fixed hole-to-hole or inter-rod distances that may not match patient anatomy and may prevent optimal occipital screw placement, compromising construct strength. These systems also have been known to experience failures (e.g., loosening, breakage, or cutout), including rod failure (breakage or telescoping), plate failure (fracture), or screw failure (breakage, migration or pullout). Moreover, in addition to the need to overcome problems of screw loosening, there exists a need for occipital plate systems for spinal stabilization in which the occipital plate:                does not obscure the surgeon's view as a screw is being inserted,        has a profile that maximizes space for graft material;        can support compression or distraction between the anchored occipital plate and other anchored components; and.        is configured to permit greater flexibility in deployment with the rods by the surgeon to achieve optimum fit.        
There are disclosed herein surgical implants, instruments and methods for occipitocervical fusion which allow independent insertion of the screw anchors as well as stable connection to the longitudinal rod, and permit greater flexibility and adjustability during surgery via a universal, polyaxial connection means for securing an occipital plate to a spinal rod or plate. It is believed that the use of the systems disclosed herein will overcome limitations noted above and that will result in improved maintenance of alignment, increased rate of successful arthrodesis, and minimized occurrence of adverse events as evidenced by clinical and radiographic outcomes.